1. Field of Endeavor
The present invention relates to thermal cycling and more particularly to instantaneous in-line heating of aqueous samples on a micro-optical-electro-mechanical system (MOEMS).
2. State of Technology
Microfluidic devices are revolutionizing environmental, chemical, biological, medical, and pharmaceutical detectors and diagnostics. “Microfluidic devices” loosely describes the new generation of instruments that mixes, reacts, fractionates, detects, and characterizes complex samples in a micro-electro-mechanical system (MEMS) circuits manufactured through standard semiconductor lithography techniques. These techniques allow mass production at low cost as compared to previous benchtop hardware. The applications' for MEMS devices are numerous, and as diverse as they are complex. Typically these devices employ aqueous solvents as the chemical reaction medium, which may or may not be partitioned into discrete segments either as “slugs” spanning the entire channel or discrete droplets emulsified in an oil flow.
As sample volumes decrease, reagent costs plummet, reactions proceed faster and more efficiently, and device customization is more easily realized. By reducing the reactor channel dimensions, supplying the requisite activation thermal energy to drive endothermic reactions on-chip becomes much faster as heat diffusion distance decreases proportional to the channel length and the thermal mass to heat decreases on the order of length cubed. However, current MEMS fluidic systems have the problem of heating not only the chemical reactor volumes within their channels (whether they be “slugs” or emulsion droplet streams), but also heating the entire substrate which is terribly inefficient for cyclical heating reactions where the heat deposited must then be quickly removed. As the reactions proceed the substrate accumulates heat, and takes much longer to cool down.
The present invention provides a method of near-instantaneous thermal energy deposition into the aqueous chemical reactor partitions or streams utilizing microwave absorption of energy from a coincident low power Co-planar waveguide (CPW) or microwave transmission line. Microwave heating of aqueous solutions exhibits excellent energy deposition due to the polarization of the water molecules. This mechanism is exploited by the ubiquitous microwave oven, and can be adapted to microscale lab-on-chip systems by innovative design and placement of microwave cavities on MEMS devices. This method provides a major improvement over prior art microfluidic channel heating methods such as joule-heating from trace resistors sputtered or electron-beamed onto the channel walls during device fabrication. The prior art methods are time-consuming and provide the associated device heat build-up described above. This not only provides the desirable cost incentive, but can cut processing times by an order of magnitude or greater, making popular on-chip process such as Polymerase Chain Reaction (PCR), in vitro protein translation, immunoassay analysis, etc. truly real time. The benefits to bacterial, viral, chemical, explosives, and other detection, as well as point-of-care diagnostics, are obvious. Also, the burgeoning field of on-chip synthesis of chemical complexes, nanoparticles, and other novel compounds relies on precise energy deposition which is ideally suited by this method.